Producing Coral Offspring with Cryopreserved Sperm: A Tool for Coral Reef Restoration

Cryopreservation is an important conservation tool, which may help reef-building coral survive. However, scaling-up from small, laboratory-sized experiments to higher-throughput restoration is a major challenge. To be an effective restoration tool, the cryopreservation methods and husbandry to produce new offspring must be defined. This study examined small and larger-scale in vitro reproduction and settlement for Acropora tenuis and Acropora millepora and found that: 1) cryopreservation of coral sperm reduced sperm motility and fertilization success in half, thus fresh sperm, capable of becoming highly motile, is key; 2) the sperm-to-egg ratio and the concentration of the cryoprotectant treatments affected fertilization success in small-and larger-scale reproduction trials using cryopreserved sperm (p < 0.05); 3) cryopreservation did not affect settlement success, as larvae produced with fresh or cryopreserved sperm had the same settlement success (p > 0.05); and 4) the residence time of the sperm within the bank was not important as the fertilization success of sperm frozen for less than 1 month was similar to that frozen up to 2 years (p > 0.05). These results described the first settlement for coral larvae produced from cryopreserved sperm and established important ground-work principles for the use of cryopreserved coral sperm for future reef restoration efforts.